Bioabsorbable surgical devices made from copolymers derived from glycolide and epsilon-caprolactone are known in the art. Such bioabsorbable surgical devices include surgical sutures.
A desirable characteristic of a bioabsorbable suture is its ability to exhibit and maintain desired tensile properties for a predetermined time period followed by rapid absorption of the suture mass (hereinafter "mass loss".)
Synthetic absorbable sutures are known in the art. Absorbable multifilament sutures such as DEXON sutures (made from glycolide homopolymer and commercially available from Davis & Geck, Danbury, Conn.), VICRYL sutures (made from a copolymer of glycolide and lactide and commercially available from Ethicon, Inc., Sommerville, N.J.), and POLYSORB sutures (made from a copolymer of glycolide and lactide and commercially available from United States Surgical Corporation, Norwalk, Conn.) are known in the industry as short term absorbable sutures. The classification short term absorbable sutures generally refers to surgical sutures which retain at least about 20 percent of their original strength at three weeks after implantation, with the suture mass being essentially absorbed in the body within about 60 to 90 days post implantation.
Long term absorbable sutures are generally classified as sutures capable of retaining at least about 20 percent of their original strength for six or more weeks after implantation, with the suture mass being essentially absorbed in the body within about 180 days post implantation. For example, PDS II sutures (commercially available from Ethicon, Inc., Sommerville, N.J.), are synthetic absorbable monofilament sutures that reportedly retain at least about 20 to 30 percent of their original strength six weeks after implantation. However, PDS II reportedly exhibits minimal mass loss until 90 days after implantation with the suture mass being essentially absorbed in the body about 180 days after implantation. MAXON suture (commercially available from Davis & Geck, Danbury, Conn.) is another absorbable synthetic monofilament that reportedly generally fits this absorption profile.
Recently, United States Surgical Corporation has introduced BIOSYN monofilament sutures which exhibit good flexibility, handling characteristics, knot strength and absorption characteristics similar to those of presently available short term absorbable multifilament sutures.
Another attempt to provide an acceptable synthetic absorbable monofilament sutures resulted in MONOCRYL, a suture fabricated from an absorbable block copolymer containg glycolide and epsilon-caprolactone, commercially available from Ethicon, Inc.
However, no synthetic absorbable monofilament sutures exist today which approximate the strength retention, mass loss, and modulus of sutures commonly referred to in the art as "catgut" or "gut" sutures. It is well known in the art that the term gut suture refers to a collagen based suture of any type or origin often fabricated from the mammalian intestines, such as the serosal layer of bovine intestines or the submucosal fibrous layer of sheep intestines. Gut sutures exhibit the unique combination of two week strength retention and about 75 day mass loss while maintaining acceptable modulus and tensile strength; and thus are still widely used in gynecological surgery.
It would be advantageous to provide a synthetic absorbable suture which exhibits physical properties similar or superior to the gut suture.
U.S. Pat. No. 4,700,704 to Jamiolkowski does teach that sutures can be fabricated from random copolymers of glycolide and epsilon-caprolactone, and more specifically from random copolymers containing from 20 to 35 weight percent epsilon-caprolactone and from 65 to 80 weight percent glycolide. Moreover, Jamiolkowski reports that sutures fabricated from glycolide/epsilon-caprolactone copolymers containing over 35% caprolactone are not orientable to a dimensionally stable fiber. Jamiolkowski further reports that some sutures fabricated from glycolide/epsilon-caprolactone copolymers containing 15% caprolactone are also not orientable to a dimensionally stable fiber. Furthermore, Jamiolkowski also reports the undesirable combination of low modulus and low tensile strength for the glycolide/epsilon-caprolactone copolymers which he was able to fabricate into sutures.
U.S. Pat. Nos. 4,045,418 and 4,057,537 disclose random copolymers obtained by copolymerizing lactide and epsilon-caprolactone as well as terpolymers obtained by polymerizing lactide, epsilon-caprolactone, and glycolide. The copolymers as well as the terpolymers disclosed in U.S. Pat. Nos. 4,045,418 and 4,057,537 have at least 60% by weight lactide. These copolymers have been described in the literature as having "one major drawback which has prevented their wide spread use. Although the copolymers can be literally interpreted to be `bioabsorbable`, the rate of absorption is so slow that it renders the copolymers practically useless for numerous medical applications" (see U.S. Pat. No. 5,468,253 at column 2, lines 24 et seq.). In fact, U.S. Pat. No. 5,468,253 addresses this problem by disclosing medical devices formed from a random copolymer of: a) from about 30 to about 50 weight percent of epsilon-caprolactone, trimethylene carbonate, an ether lactone and combinations thereof, and b) the balance being substantially glycolide or para-trimethylene carbonate.
Therefore, it would be unexpected that medical devices such as sutures made from random copolymer of glycolide, epsilon-caprolactone, trimethylene carbonate, and lactide would provide the strength retention and mass loss characteristics approximating those of gut sutures while maintaining an acceptable modulus and tensile strength.